At one stage in the replication of optical discs such as DVDs (Digital Versatile Discs, also referred to as Digital Video Discs), two clear polycarbonate half-discs are bonded together, for example using an ultraviolet curable resin, to form the assembled disc. The bonding of the two half-discs is referred to as the Pairing Process. Prior to bonding, the surface of at least one of the half-discs is coated with a reflective layer of aluminum to enable the disc to reflect laser light in a DVD player. Similar techniques are used for other types of optical discs.
In a Pairing Process, ultraviolet curable resin is deposited on one of the half-discs and then the two half-discs are brought together with their mating surfaces at an acute angle to each other. The angle between the half-discs is then decreased so that the ultraviolet curable resin is distributed across the mating surfaces of the half-discs.
One disadvantage of this approach is the high complexity of the control system that controls the motion of the half-discs. The motion is typically specified in advance using a large number of parameters. The high complexity of the motion control machinery increases the time spent maintaining and repairing equipment.
A further disadvantage of this approach is that air bubbles can be trapped between the mated surfaces of the half-discs. These bubbles reflect laser light and can cause the disc to be rejected. This, in turn, reduces the yield of the replication process. The number of bubbles can be reduced by applying the ultraviolet curable resin and paring the half-discs in an evacuated enclosure. However, a large enclosure is required to accommodate all of the equipment. The time spent removing air from the large enclosure and moving half-disc in and out of the chamber results in a relatively slow process. The process is further complicated by the need to apply the ultraviolet curable resin into the vacuum.